NF Question 20

[Deep]

Here's another play. Instead of having a kick that bounces back behind the line, let's just have the kick go straight up and be caught behind the line. Suppose that B1 signals for a fair catch during the kick, then he could not block until the kick ends. The kick would end when it was caught behind the line, but the down would not.

So PSU213 & albamabluezebra, I think you are absolutely correct. And albamabluezebra, the key must be wrong as you suspect.

I like the college rule better, it's more straightforward.